Defrostable refrigeration system



Feb. 10, 1953 E. w. zEARFoss, JR 2,627,730

DEFROSTABLE REFRIGERATION SYSTEM Filed Dec. 9, 1950 N 1 I F K 2! INVENTOR.

Patented F eb. 10, 1953 UNITED STATES PATENT OFFICE DEFROSTABLE REFRIGERATION SYSTEM Application December 9, 1950, Serial No. 200,019

2 Claims.

The invention hereinafter disclosed and claimed has to do with refrigeration apparatus and, more particularly, is concerned with apparatus of the type having provision for heating the evaporator to effect removal of frost deposited upon the surfaces of said evaporator.

Periodic removal of accumulated frost is necessary in order to maintain the efficiency of a refrigeration machine the evaporator of which is operating at temperatures below the freezing point of water, and such defrosting has frequently been accomplished by shutting down the re frigeration system. Since extended discontinuities of operation of the system result in thawing of frozen foods contained within the evaporator, with resultant deterioration of such foods, and since the defrosting operation has frequently been troublesome and time-consuming, auto-- matic and relatively frequent defrosting of the evaporator is desirable. Such defrosting can conveniently be accomplished by subjecting the evaporator to a considerable quantity of heat over a relatively short period of time, and the most desirable and efficient modes of accomplishing this have incorporated heat pump principles. It is with improvements in this class of apparatus that the present invention is concerned.

It has been known to effect defrosting by bypassing the condenser and restrictor of the refrigerating system and delivering directly to the evaporator hot gaseous refrigerant flowing from the compressor. Such arrangements are intended to result in condensation of the gaseous refrigerant within the evaporator, with resultant heating and consequent defrosting of the latter. Such systems have, however, not proven satisfactory in practice due to the fact that, under defrosting conditions, that is, when the condenser and the restrictor are by-passed, insuihcient liquid refrigerant is available in the system. As a result of this insufficiency of liquid refrigerant, and as is explained hereinafter, the hot gas introduced into the evaporator, while it tends to condense therein, becomes trapped in said evaporator as liquid and must then re-evaporate therein prior to flowing through the suction line to the compressor. Since the condensation process involves the liberation of only slightly more heat than is taken up during the re-evaporation process, the net heat available for defrosting, in arrangements in which the condensate tends to become trapped in the evaporator, is relatively slight being approximately equal only to the degree of superheat within the gaseous refrigerant.

Attempts have been made to improve systems of this type, although there has been no recognition of the causes which underlie the difiiculties encountered, by adding to the system a complicated arrangement of valving and connections intended to modify the normal flow of refrigr erant within the system and, while certain of these attempts have yielded useful results, such approaches to the problem are inherently undesirable from the standpoint of high initial cost and unreliability in service.

I have discovered that it is essential that a substantial quantity of refrigerant be circulated during the defrosting process, and that only in this way can the re-evaporation process be divorced from the evaporator and caused to take place in the suction line and the compressor housing.

With the foregoing diificulties in mind, and recognizing the problems which underlie the deficiencies of prior arrangements, it is the primary object of the present invention to provide a heat pump defrosting system which is not only highly effective in producing adequate defrosting in unusually short periods of time, but which system is of the simplest and most inexpensive type.

More specifically, the invention contemplates provision of a very simple defrosting system in which the circulation and distribution of refrigerant within the elements of the refrigeration machine are such that, during the defrosting cycle, only condensation occurs within the evaporator and substantially all of the evaporation process takes place within the suction line and the compressor housing.

In the achievement of the foregoing general objectives, the apparatus of the invention utilizesin novel combination with a by-pass conduit or connection serving to deliver hot gaseous refrigerant to the evaporator-a sump or accumulator disposed within the system between the restrictor and the evaporator and serving, under normal refrigerating conditions, to collect a quantity of liquid refrigerant therein. In particular accordance with the invention, the bypassed gaseous refrigerant is delivered to this accumulator, when defrosting of the evaporator is desired, with the result that the amount of refrigerant, by volume, which flows through the accumulator is increased many-fold and this increased volumetric flow serves, in a manner which will be more particularly described hereinafter, to drive the stored liquid refrigerant from the accumulator and to cause said liquid refrigerant to pass through the evaporator and t0 be returned to the compressor where it is evaporated and re-introduced into the accumulator in gaseous form, from whence it passes to the evaporator.

It is also a feature of the present invention that initiation of the defrosting operation may be accomplished by the use of any one of a number of simple and inexpensive devices adapted to modify the normal flow of refrigerant within the system and to establish the aforesaid flow of hot gaseous refrigerant through the mentioned bypass conduit. such means may be exceedingly simple in nature, comprising nothing more, for example, than a solenoid-actuated valve disposed in the by-pass conduit.

The foregoing objects and features of my invention, together with significant details of construction thereof, will be understood from a consideration of the following description taken in conjunction with the accompanying drawing, the single figure of which is a diagrammatic representation of a refrigeration system including defrosting apparatus embodying the present invention.

Now making detailed reference to the drawing, it will be seen that the illustrated embodiment of the invention includes the elements of a refrigeration system of conventional type, said system having a compressor 13, a condenser H, a continuously open restricted connection, or capillary tube [2 (other suitable control devices could be used if desired), and an evaporator it which is disposed in heat exchange relation with a compartment or zone to be cooled, said compartment being diagrammatically represented by the broken line identified at I i. The aforesaid elements are connected in series flow circuit through the agency of suitable conduits and connections, including the aforesaid capillary tube and a suction line illustrated at l5. understood, the capillary tube I2 and the suction line l5 may, if desired, be disposed in heat exchange relation, but such disposition has been omitted from the disclosure in the interest of simplicity in illustration. The normal operation of such a system is well known and requires no detailed description herein.

In especial accordance with the present invention, however, the apparatus includes a by-pass connection or conduit I6, in novel combination with an accumulator device effective to insure such distribution of refrigerant within the sys-. tem, during defrosting of the evaporator l 3, that a substantial amount of liquid refrigerant is made available at the compressor as soon as the defrosting process is initiated, and the resultant flow of refrigerant through the system is such that substantially no re-evaporation of condensed refrigerant takes place within the evaporator. The said device comprises a sump or accumulator shown at I1 and conveniently takes the form of a sealed tank to which, under normal refrigerating conditions, is delivered liquid refrigerant flowing through the capillary tube l2. Delivery of such liquid refrigerant to the accumulator is effected through the agency of a short connection [8 which is coupled to the capillary tube 12 and which connection preferably includes a drier, as shown at l9 in the drawing.

Disposed within the accumulator is a vertically extending pipe or conduit 28, the lower end of which is open and which pipe is provided with an aperture 2i near the upper portion thereof, that is, adjacent the top of the accumu- As will be A lator vessel. As will presently appear, liquid refrigerant derived from the capillary tube 12 accumulates in the sump to approximately the level indicated in the drawing under normal conditions of operation, and flows to the evaporator 13 through the aforesaid aperture 2| and through a short feed line 22 which forms an extension of the pipe 26. The lay-pass conduit I6, which is preferably controlled by a solenoidactuated valve represented at 23, has its upper end in open communication with the space within the accumulator.

A circuit adapted to control actuation of the valve, as well as energization of the compressor I0, is also illustrated and its operation will be described just below. It should be understood, however, that the invention is not limited to the use of a solenoid-actuated valve for controlling the flow of refrigerant through the bypass 15 and that, insofar as initiation of the defrosting operation is concerned, the control circuit may take any desired one of a number of known forms.

As is common practice, energization of the compressor is controlled in accordance with the determinations of a temperature-sensitive switch device 2%, responsive to the pressure of a vaporizable fluid contained within a feeler bulb (not shown), which bulb is generally disposed in heat exchange relation with the evaporator, or with the space to be cooled. As will be understood Without detailed description, closing of the switch device 26 places the motor of the compressor across the line 25. During normal operation of the system, that is when defrosting is not required, the compressor IE3 then delivers hot gaseous refrigerant to condenser H through the compressor discharge connection 25. The usual change of state occurs in the condenser, and the resultant liquid refrigerant is fed toward the evaporator H5 through the capillary tube I2. As a result of the pressure changes occurring within the capillary tube, a mixture of liquid refrigerant and flash gas is delivered to accumulator ll through connection 8. The refrigerant emitted from the capillary tube comprises a mixture of liquid and gas, the amount of refrigerant in the liquid phase being very much in excess of that which is in the vapor phase. This refrigerant is trapped in the accumulator and the liquid component being heavier than the gaseous component gradually accumulates until the level thereof reaches the aperture 2| provided in pipe 26. The size of the aperture 28 is so proportioned, with respect to the aforesaid flow of refrigerant into the accumulator, that the pressure drop across the aperture is less than the hydrostatic head determined by the height of the aperture 2! above the bottom wall of the accumulator. The size of the aperture, it should be noted, is not critical,

a 16 aperture having given satisfactory results in a representative embodiment of the invention.

When, as above indicated, the level of liquid refrigerant within the accumulator I? reaches the aperture 2!, the pressure maintained within the accumulator by the presence of the flash gas introduced from the capillary tube forces liquid refrigerant through the said aperture and into the feed line 22 from whence it flows to the evaporator 13. During the normal cycle, the accumulator remains full of liquid to the approximate height of said aperture.

Liquid refrigerant is, of course, vaporized in the evaporator l3, producing the desired refrigeration effect, and the resultant cool, relatively low pressure gas is returned to the compressor ID by way of the suction line I5. The switch device 2% energizes the compressor and effects the aforesaid normal circulation of refrigerant within the system, cyclically, in response to the determinations of the feeler bulb associated with the said switch device 24.

The control circuit of the illustrated embodiment includes a single throw, double pole switch 21, and the defrosting cycle is initiated in response to closure of this switch, regardless of the position of the contacts of switch device 24. As will be understood, the switch shown diagrammatically at 2'! is indicative of the fact that the invention contemplates inclusion of such apparatus as may be required to initiate and terminate the defrosting cycle. Preferably, although not necessarily, switch 21 may be actuated automatically in a variety of different ways such, for example, as by the use of a frost thickness switch device of the type described and claimed in applicants co-pending disclosure bearing Serial No. 183,757, filed September 8, 1950.

The aforesaid closing of the switch 2'! places.

the valve 23 across the line 25, thereby opening said valve and, concurrently, energizing the compressor. It will be noted that the circuit arrangement is such that energization of the compressor is accomplished even in the event that the contacts of switch device 2G should be open when defrosting is initiated.

When modified flow of refrigerant has been established within the system, by opening of the Valve 23, hot gaseous refrigerant flows to the accumulator, by-passing the condenser If and the restrictor l2. While it is desirable that the hot gaseous refrigerant by-pass the condenser I I, as well as the restrictor l2, by-passing of the condenser may if desired be omitted. Such modification of the apparatus only requires relocation of the point at which one end of the conduit I6 is connected in the system. Under such modified conditions all of the refrigerant entering the accumulator is in the vapor phase and, by comparison with the foregoing description having to do with introduction of refrigerant to the accumulator during the normal cycle, it will be seen that the amount of refrigerant (by volume) entering the accumulator is increased to a value many times as great as the amount, in terms of volume, which was flowing into the accumulator during the normal cycle. This increase flow cannot be accommodated by aperture 2 l, with the result that the pressure drop across said aperture is increased to a degree such that the hydrostatic pressure of the liquid within the accumulator is overcome and the liquid is forced into the bottom of tube 25 and, together with a portion of the gaseous refrigerant which has just been delivered to the accumulator, flows through the said line 22 and into the evaporator.

This liquid refrigerant floods the evaporator and flows into the suction line and the compressor housing. As it leaves the evaporator, it is replaced by hot gaseous refrigerant flowing through the by-pass conduit i6 and the accumulator ll, which has now been emptied of liquid, such gaseous refrigerant being at an elevated temperature and giving up its heat to the frost-laden evaporator with the result that condensation occurs within the evaporator. This condensation of gaseous refrigerant takes place in the evaporator at a temperature (and corresponding pressure) just above 32 F., since the temperature of the evaporator cannot rise materially above this value until all of the frost has been melted. It will be understood that defrosting is accomplished by the aforesaid heat transfer which.

perature, in the suction line I5 and the low pressure housing of the compressor 10, has been evaporating and the gas thus formed is forced by the compressor through the by-pass conduit it from whence it is again delivered to the evaporator, being available to continue the condensation process therein.

As will be recognized, the heat required to vaporize the returned liquid is supplied by the thermal mass of the compressor, by heat exchange between the compressor and the ambient air, and by the electrical losses which inevitably occur in the compressor.

Passage of sumcient quantities of liquid refrigerant into the suction line and the housing of the compressor operates to raise the suctionpressure, at the evaporator, above that value which corresponds to the 32 F. temperature maintained at the evaporator because of the presence of meltable frost thereon. When the f suction pressure reaches the stated value, hot

gaseous refrigerant introduced within the 32 F. evaporator, once it has condensed, cannot re-' evaporate since the suction pressure is at a value which precludes evaporation at 32 F. Considered from another point of view, it will be understood that the presence of liquid refrigerant in the suction line and in the compressor housing, as contemplated by the invention, satisfies the pumping capacity of the compressor and the compressor does not therefore operate to evaporate liquid refrigerant in the evaporator.

It will be noted that the over-all process described above diifers very materially from that which would occur were the accumulator not present in the circuit. In the absence of the accumulator, the hot gaseous refrigerant delivered to the evaporator would also tend to condense, but, concurrently, the suction of the compressor, as in the normal cycle, would operate to re-evaporate the condensate within the evaporator and withdraw refrigerant from the evaporator in gaseous form. Since condensation and evaporation represent opposite processes of heat transfer, the net heat flow to the evaporator, and hence the net defrosting effect would be very slight, and it is precisely this difiiculty which was encountered in the arrangements of the prior art. Therefore the use of the by-pass conduit [6, in novel combination with the accumulator I1, serves to prevent the re-evaporation process from taking place within the evaporator and causes it to occur in the suction line and in the compressor housing. Thus the condensation process occurring within the evaporator is not opposed by re-evaporation, and hence the heat transfer to the evaporator is substantial and rapid defrosting thereof takes place.

From the foregoing description it is clear that the present invention provides a heat pump defrosting system which is characterized by a high degree constructional simplicity and by unusual rapidity in operation. No electrical heating devices are employed and the consumption of power, during the defrosting operation, is unusually low.

I claim:

1.In a refrigeration system having compressor, condenser, restrictor and evaporator elements normally so connected that refrigerant flows through said elements in the order named whereby to vaporize refrigerant within said evaporator, means for modifying the flow of refrigerant through said system to cause condensation of refrigerant within the evaporator and consequent heating of the latter, comprising: conduit means by-passing said restrictor and operable to deliver to said evaporator hot gaseous refrigerant flowing from the compressor, to effect the aforesaid condensation and consequent heating of the evaporator; and apparatus adapted to increase the quantity of liquid refrigerant active in the system under the aforesaid modified condition of operation, said apparatus comprising a vessel with an upper portion of which said restrictor is in open communication, said vessel further being connected to said evaporator through the agency of a pipe having an opening communicating with a lower sump portion of the vessel, said vessel serving, under normal conditions of operation, to collect liquid refrigerant within said lower sump portion to a level well above the said pipe opening, and said conduit means being in communication with an upper portion .of said vessel and delivering thereto, under said modified condition of operation, hot gaseous refrigerant whereby to drive liquid refrigerant contained in said accumulator through said pipe opening and into said evaporator, under the influence of pressure exerted by said gaseous refrigerant against the free surface of liquid refrigerant contained within said vessel; and means normally preventing flow of gaseous refrigerant through said conduit means and operable to establish said modified flow of refrigerant within the system by permitting flow of gaseous refrigerant through said conduit means.

2. In a refrigeration system of the type having elements including a compressor, a condenser, a restrictor, an evaporator, and conduit means connecting said elements in series flow circuit, means including a valve-controlled line icy-passing said restrictor and communicat ing with said evaporator and being operable to interrupt normal flow of liquid refrigerant through the restrictor and thence to the evaporator, and to establish modified flow of hot gaseous refrigerant through said line and to said evaporator, and a sump disposed in the circuit between said restrictor and said evaporator and functioning, under the said conditions of normal flow, to collect a quantity of liquid refrigerant therein, said line being associated with said sump so that the stated flow of hot gaseous refrigerant through said line causes flow of liquid refrigerant contained in said accumulator through said evaporator and toward said compressor.

ELMER W. ZEARFOSS, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,451,682 Lund Oct. 19, 1948 2,455,421 Kirkpatrick Dec. '7, 1948 2,459,173 McCloy Jan. 18, 1949 

